Digital electronic scale with stabilized display

Abstract

System and method for providing a stable digital display of a value which fluctuates such as the input signal produced by a moving load on an electronic weighing scale. Digital readings are integrated over time, and the variations in the digital readings become insignificant compared to the sum of the readings in the historical average. Weight readings are automatically calibrated for span and linearization.

I claim: 
     
       1. In a method of determining the weight of a moving load on the load receiving member of a scale, the steps of: providing an input signal corresponding to the weight of the load; periodically sampling the input signal; checking each sample to determine whether the input signal is varying by more than a predetermined amount; if the input signal is varying by less than the predetermined amount, averaging the current sample with a predetermined number of previous samples to provide a running average of the input signal, and displaying the running average; if the input signal is varying by more than the predetermined amount, averaging the current sample with all previous samples for which the input signal varied by more than the predetermined amount to provide a historical average of the input signal, displaying the historical average, placing two loads of known weight on the load receiving member, combining the input signals produced by a zero load and the two loads of known weight to determine span and linearity factors for the scale, and combining the span and linearity factors with the input signal produced by a load to be weighted to provide a calibrated weight signal. 
     
     
       2. In a scale for weighing a moving load: a load receiving member, means including a load cell connected to the load receiving member for providing an input signal corresponding to the weight of the load, means for checking the input signal to determine whether the input signal is varying by more than a predetermined amount, means active when the input signal is varying by less than the predetermined amount for averaging the current value of the input signal with a predetermined number of previous values to provide a running average of the input signal, means active when the input signal is varying by more than the predetermined amount for averaging the current value of the input signal with all previous values for which the input signal varied by more than the predetermined amount to provide a historical average of the input signal, display means for displaying the running average when the input signal is varying by less than the predetermined amount and displaying the historical average when the input signal is varying by more than the predetermined amount, and calibration means responsive to the input signals produced by a zero load and two loads of known weight on the load receiving member for determining span and linearity factors for the scale and combining the span and linearity factors with the input signal produced by the load to be weighed to provide a calibrated weight signal. 
     
     
       3. The scale of claim 2 wherein the span factor is determined by the relationship ##EQU2## where A is the span factor, W 2  is the input signal produced by the greater load of known weight, Z is the zero load input signal, and R is the resolution of the scale; the linearity factor is determined by the relationship ##EQU3## where B is the linearity factor and W 1  is the input signal produced by the smaller load of known weight; and the calibrated weight signal is determined by the relationship   W.sub.c =A[(W-Z)±B(W-Z).sup.2 ],     where W c  is the calibrated weight signal and W is the input signal produced by the load to be weighed.   
     
     
       4. In a scale of weighing a load: a load receiving member, means including a load cell connected to the load receiving member for providing an input signal corresponding to the weight of the load, calibration means responsive to the input signals produced by a zero load and two loads of known weight on the load receiving member for determining span and linearity factors for the scale and combining the span and linearity factors with the input signal produced by the load to be weighed to provide a calibrated weight signal, and display means responsive to the calibrated weight signal for indicating the weight of the load. 
     
     
       5. The scale of claim 4 wherein the span factor is determined by the relationship ##EQU4## where A is the span factor, W 2  is the input signal produced by the greater load of known weight, Z is the zero load input signal, and R is the resolution of the scale; the linearity factor is determined by the relationship ##EQU5## where B is the linearity factor and W 1  is the input signal produced by the smaller load of known weight; and the calibrated weight signal is determined by the relationship   W.sub.c =A[(W-Z)±B(W-Z).sup.2 ],     where W c  is the calibrated weight signal and W is the input signal produced by the load to be weighed.